Only problem I've been having is that previewing a comment on a thread with YouTube ends up redirecting the browser to the YouTube home page. The only fix has been to not preview, just Post Quick Reply.

If you view the response headers in a browser that loads the page, you can see why it's saying this. When you click that link, the first thing it does is a 302 redirect to m3post.com, since that's the actual domain you want. In order to do the redirect, it sets the Location header. Once it loads that same url on m3post.com, it performs a second 302 redirect. This second redirect is because of the "goto=newpost", it changes the url to the one that takes you directly to the newest post. But it has to set the Location header again to do this. So now the browser thinks the location was changed twice, and some of them don't like it.

Further proof, if you go to m3post.com directly, it can do the redirect properly: